1. Field of the Invention
The invention relates to an optical scanner, and more particularly, to an optical scanner for controlling electric power supplied to a cold cathode ray tube according to its status.
2. Description of the Prior Art
Generally, an optical scanner conserves power by regulating electric power supplied to the light source based on scanner status. The optical scanner power regulation method (Taiwan patent number 283818) relates to a method for controlling the power supplied to the cold cathode ray tube of an optical scanner. During scanning, the power supply of the cold cathode ray tube is maintained at a high voltage. When the scanner is idle, the power supply of the cold cathode ray tube is maintained at a low voltage to save energy.
Please refer to FIG. 1. FIG. 1 is a functional block diagram of a prior art optical scanner 10. The optical scanner 10 comprises a signal control device 12, a warming power generator 14, and a cold cathode ray tube 16. The signal control device 12 is a digital/analog converter. Different digital control signals are inputted into the signal control device 12 through the input ports 11, and different voltage values are outputted from output ports 13 of the signal control device 12 to the warming power generator 14. The warming power generator 14 comprises an operation magnifier 18, a darlington transistor 19, and an alternate/direct ascending voltage circuit 20. The voltage is processed by the operation magnifier 18 and darlington transistor 19 to produce a warming direct voltage 15. The value of the voltage 15 represents the warming time of the cold cathode ray tube 16. During warming up of the cold cathode ray tube 16, the electric power is supplied at a low voltage. This saves energy.
Please refer to FIG. 2. FIG. 2 is a diagram showing the relationship between the digital control signals of the optical scanner 10 and the warming time of the cold cathode ray tube 16. A warming time is selected after use of the optical scanner 10 is completed. As shown in FIG. 2, when the digital control signals inputted into the input ports 11 of the signal control device 12 are 110, the warming time of the cold cathode ray tube 16 is five seconds. When the digital control signals are 000, the warming time of the cold cathode ray tube 16 is 180 seconds.
The prior art optical scanner 10 is complex and expensive. Accurate selection of a warming time is subject to human error. If an excessively long warming time is selected, the wait time is also excessive. On the other hand, electric power is wasted if the warming time selected is too short.
It is therefore a primary objective of the present invention to provide an optical scanner for controlling electric power supplied to a cold cathode ray tube according to its status.
Briefly, in a preferred embodiment, the present invention provides an optical scanner comprising:
a scanning module for scanning a document to generate corresponding image signals;
a cold cathode ray tube for supplying lights to the document when scanning the document;
a power source for supplying electric power to the cold cathode ray tube; and
a control circuit for controlling operations of the scanner;
wherein when the scanning module is in an idle state, the control circuit controls the active period of each of the power source""s duty cycles to reduce the electric power supplied to the cold cathode ray tube so that the cold cathode ray tube can be maintained in a warm state and the startup time for warming the cold cathode ray tube to scan the document is reduced.
It is an advantage of the present invention that the scanner provides an effective method for saving power by controlling the length of time power is supplied. The warming time is shorter if the scanner starts scanning after being idle. The optical scanner is simple to produce inexpensively.
These and other objects and the advantages of the present invention will no doubt become obvious to those of ordinary skill in the art after having read the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.